Color image processing apparatus

ABSTRACT

An image conversion apparatus for image-converting input color image signals, and outputting the converted signals to an output apparatus, allows execution of a plurality of different color processing operations, checks if an input color image falls within a color reproduction region of the output apparatus, and changes the color conversion processing result to be output depending on whether or not the input color image falls within the color reproduction region of the output apparatus. For example, when the input color image falls within the color reproduction region of the output apparatus, color reproduction color-matched with input color image signals is performed. When the input color image falls outside the reproduction region, color reproduction is performed by color conversion processing assuring highest color reproducibility.

This application is a division of application Ser. No. 08/460,090, filedJun. 2, 1995, pending, which was a continuation of application Ser. No.07/772,154, filed Nov. 14, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color image processing apparatus forconverting an input color image signal into an output color imagesignal, and outputting the output color image to an output apparatus forprocessing the converted color signal and, more particularly, to a colorimage processing apparatus for converting an input color image signalbased on an additive color process into a color image signal based on asubtractive color process.

2. Description of the Prior Art

In a conventional color image copying apparatus, as shown in FIG. 19, R,G, and B digital image signals based on the additive color process andinput by an image input apparatus 401 are converted into color imagesignals based on the subtractive color process through a log conversioncircuit 402, a masking circuit 403, and a blackening/UCR circuit 404.The converted image signals are printed with toners or inks by an imageoutput apparatus 405.

More specifically, the log conversion circuit 402 converts the R, G, andB signals into cyan (C), magenta (M), and yellow (Y) as complementarycolors.

The masking circuit 403 serves as a matrix calculation circuit forcorrecting unnecessary absorption of an ink or toner printed by theimage output apparatus 405. The blackening/UCR circuit 404 replacesequivalent neutral components in Y, M, and C color signals into a black(K) signal.

R, G, and B digital image signals based on the additive color processand input by the image input apparatus 401 are converted into colorimage signals based on the subtractive color process through the logconversion circuit 402, the masking circuit 403, and the blackening/UCRcircuit 404. The converted image signals are supplied to the imageoutput apparatus 405, and are printed with inks or toners as colorimages.

In general, colors of a printed matter or a photograph as a color imageoriginal, or an image displayed on a CRT are distributed in wider regionon a color spatial coordinate system than a color reproduction regionobtained by mixing toners or inks of an image output apparatus.

In order to realize optimal color reproduction for all the colors ofinput color image signals, compression processing on a color space isusually executed for providing a gradation characteristic also to colorsoutside the color reproduction region.

More specifically, color reproduction outside the color reproductionregion is projected onto the color reproduction region, and in order toprovide a gradation characteristic to an image, compression mapping of acolor space is performed. As a result, colors are reproduced to beslightly different from original colors.

FIG. 20 shows conventional compression mapping on the color space (onthe a*-b* coordinate system). In FIG. 20, a region surrounded by a solidcurve represents a color space region of a color image original, and adotted curve inside the solid curve represents the color reproductionregion of the image output apparatus. FIG. 20 reveals that an inputcolor original exceeds the color reproduction region of the image outputapparatus.

Conventionally, color reproduction outside the color reproduction regionis projected onto the color reproduction region, as indicated by arrows.In order to provide a gradation characteristic to the image, colors arereproduced to be slightly different from original colors, as indicatedby arrows. In other words, compression mapping of the color space isperformed.

Otherwise, all the images that exceed the color reproduction region ofan output apparatus such as a printer, are subject to the same colorconversion processing regardless of input image signals.

Other problems in the prior art is that, even when the color spatialdistribution of a color image original is within the color reproductionregion of the image output apparatus, and the reproduction of the samecolors as the original colors is possible, compression-mappedreproduction colors are undesirably obtained, which are different fromoriginal colors.

When a color image original is an output image from a copying apparatusor an image output apparatus (to be referred to as a grandchild copy ora generation copy hereinafter), further compressed reproduction colorsare obtained. Upon repetition of grandchild copy, reproduction colorsare compressed repeatedly, and become further different from those of animage original.

The arrows in FIG. 20 represent traces of reproduction colors.

Furthermore, in an original image wherein the color spatial distributionof a color image original is within the color reproduction region of theimage output apparatus, and gradation-expression is made within a smallregion on the space, e.g. in a gradational contour presentation ofmountains or seas on the map, the gradation characteristic may disappearby compressed reproduction.

Other shortcoming of the prior art is that, since images exceeding thecolor reproduction region of the output apparatus are subject to thesame processing regardless of extent of excess color reproduction may beimpaired in view of the gradation characteristic, or gradation maydisappear.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems. More specifically, the present invention has been made toachieve the following objects.

It is an object of the present invention to perform color reproductionin accordance with the distribution of colors of an original on a colorspace, and the color reproduction region of the output apparatus.

It is another object of the present invention to perform above-describedcolor reproduction at high speed.

It is still another object of the present invention with a simpleconstruction.

It is still another object of the present invention to improve thequality of a generation copy.

It is still another object of the present invention to provide an imageprocessing apparatus, which comprises, as an arrangement of a colorreproduction processing system for a color image original, in additionto a conventional color space compression mapping reproduction system, acolor reproduction system capable of performing reproduction of the samecolors as the original color image as to colors within a colorreproduction region of an image output apparatus, so that a processingsystem can be selected in accordance with the distribution of colors ofan original on a color space coordinate system upon reading of theoriginal, and optimal color reproduction can be realized according tooriginals.

It is another object of the present invention to provide an imageprocessing apparatus, which counts the number of colors of inputsignals, and the number of post-processing colors, and selects colorconversion processing, which, for example, can minimize a decrease inthe number of colors, in accordance with the count results, so thatoptimal conversion processing can be executed in accordance with aninput image, and the best outputs can be obtained.

Furthermore, it is still another object of the present invention toprovide an image processing apparatus, which has parameter groups ofcolor reproduction processing of a color input image not only for onecolor space compression mapping reproduction system but also for aplurality of compression ratios, and selects a parameter group for anoptimal compression ratio in accordance with the distribution of colorsof input color image signals in the color space, or selects a parametergroup for an optimal compression ratio in accordance with a distancebetween the color space coordinate system of input color image signalsand the barycentric coordinate system of the color reproduction regionof an output apparatus, thereby realizing better color reproduction.

It is still another object of the present invention to provide an imageprocessing apparatus, which directly executes, e.g., conversionprocessing of input color image signals based on the additive colorprocess and color-separated by CCDs so as to determine whether or notthe input signals are those allowing image formation, and can realizeoptimal color reproduction according to the determination result. Forexample, when it is determined that image formation is enabled, theimage processing apparatus directly converts the input image signalsinto color image signals based on the subtractive color process withreference to, e.g., a density conversion table. Contrary to this, whenit is determined that image formation of the input color image signalsbased on the additive color process is difficult to perform, the inputimage signals are processed by, e.g., conventional masking processing.In this manner, a processing system can be selected in accordance withthe distribution of colors of an original on the color space coordinatesystem, and optimal color reproduction can be realized according to theoriginal.

It is still another object of the present invention to provide an imageprocessing apparatus, which can select an optimal color image processingsystem in accordance with the distribution of colors of input colorimage signals on a color space coordinate system, and can realizeoptimal color reproduction in accordance with the input color imagesignals.

It is still another object of the present invention to provide an imageprocessing apparatus, which comprises, as an arrangement of a colorreproduction processing system for a color image original, a colorreproduction system capable of performing color reproductioncolor-matched with a color image original only within a colorreproduction region of an image output apparatus in addition to aconventional color space compression mapping reproduction system, sothat a processing system can be selected in accordance with thedistribution of colors of an original on a color space coordinate systemupon reading of the original, and optimal color reproduction can berealized according to originals.

As means for achieving the above objects, the image processing apparatuscomprises the following arrangement.

More specifically, the image processing apparatus comprises colorreproduction region storage means for storing a color reproductionregion of an output apparatus on a color space, and conversion means forconverting input color image signals obtained by reading a color imageoriginal, into output color image signals by at least two kinds ofmethods depending on whether or not the input color image signals arewithin the color reproduction region stored in the color reproductionregion storage means.

For example, at least one method of the conversion means is conversionprocessing for performing compression on the color space so that animage outside the color reproduction region of the output apparatus canalso have a gradation characteristic. At least one method of theconversion means is conversion processing for performing colorimetriccolor-matching between an image original and an output image within thecolor reproduction region of the output apparatus.

Furthermore, at least one method of the conversion means is conversionprocessing for performing enlargement on the color space, so that acolor space region of an image original is widened within the colorreproduction region of the output apparatus to obtain reproductioncolors of an output image.

In the above arrangement, as an arrangement of a color reproductionprocessing system of a color image original, a color reproductionprocessing system for performing color reproduction color-matched with acolor image original only within the color reproduction region of theimage output apparatus is arranged in addition to a conventional colorspace compression mapping reproduction system. Thus, a processing systemcan be selected in accordance with the distribution of colors of anoriginal on the color space coordinate system upon reading of theoriginal, and optimal color reproduction can be realized according tothe original.

A color image processing apparatus for converting input color imagesignals based on an additive color process into color image signalsbased on a corresponding subtractive color process, comprises firstdetection means for detecting the number of different colors using atleast some of the input color image signals based on the additive colorprocess, conversion means for converting the input color image signalsbased on the additive color process into the color image signals basedon the corresponding subtractive color process by at least two methods,second detection means for detecting the numbers of different colors, inunits of methods, of the color image signals based on the subtractivecolor process converted by the conversion means, difference calculationmeans for calculating differences between the numbers of colors detectedby the second and first detection means, and selection means forselecting the color image signals converted by the method of theconversion means corresponding to the smallest difference calculated bythe difference calculation means.

With the above arrangement, the number of colors of the input signals,and the number of post-processing colors are counted, and colorconversion processing, which, for example, can minimize a decrease inthe number of colors, is selected, so that optimal color conversionprocessing can be executed according to an input image, and the bestoutput can be obtained.

Furthermore, the color image processing apparatus comprises colorprocessing means for converting input color image signals into outputcolor image signals, and outputting the output color image signals,storage means for dividing a color space in units of predeterminedregions, and storing to which areas in the color space the input colorimage signals based on the additive color process belong, count meansfor counting the number of pixels belonging to each region of the inputcolor image signals in units of regions on the basis of the storagecontents of the storage means, and selection means for selectingconversion processing parameters of conversion means in accordance withthe count results of the count means, wherein the conversion meansconverts the input color image signals into the output color imagesignals in accordance with the parameters selected by the selectionmeans.

Alternatively, the color image processing apparatus comprises colorprocessing means for converting input color image signals based on anadditive color process into color image signals based on a correspondingsubtractive color process, and outputting the converted color imagesignals, conversion means for converting the input color image signalsbased on the additive color process into a predetermined color spacecoordinate system, calculation means for calculating a distance betweenthe coordinate position converted by the conversion means and a centralcoordinate position of a color processing region, which can be output byan output apparatus, and selection means for selecting conversionprocessing parameters of the color processing means in accordance with acalculation result of the calculation means, wherein the colorprocessing means converts the input color image signals based on theadditive color process into the color image signals based on thecorresponding subtractive color process in accordance with theparameters selected by the selection means.

In the above arrangement, the color image processing apparatus hasparameter groups of color reproduction processing of a color input imagenot only for one color space compression mapping reproduction system butalso for a plurality of compression ratios, and selects a parametergroup for an optimal compression ratio in accordance with thedistribution of colors of input color image signals in the color space.

The color image processing apparatus has parameter groups of colorreproduction processing of a color input image not only for one colorspace compression mapping reproduction system but also for a pluralityof compression ratios, and selects a parameter group for an optimalcompression ratio in accordance with the distance between the colorspace coordinate system of input color image signals and the barycentriccoordinate system of the color reproduction region of an outputapparatus, thereby realizing better color reproduction.

Furthermore, a color image processing apparatus for converting inputcolor image signals based on an additive color process into color imagesignals based on a corresponding subtractive color process, andoutputting the converted color signals to an output apparatus forprocessing the color signals, comprises conversion means for convertingthe input color image signals based on the additive color process intocolor image signals based on the corresponding subtractive color processby at least two processing methods, a look-up table for storing whetheror not the input color image signals correspond to a combination ofsignals within a color reproduction range obtained by the outputapparatus, determination means for determining, based on the look-uptable, whether or not the input color signals fall within the colorreproduction range of the output apparatus, and selection means forselecting a conversion method of the conversion means according to thedetermination result from the determination means. For example, theconversion means performs colorimetric color-matching between an inputcolor image and an output converted image within the color reproductionrange of the output apparatus.

The conversion means performs compression on the color space so as toprovide a gradation characteristic also to colors outside the colorreproduction region of the output apparatus.

In the above arrangement, direct conversion processing of input colorimage signals based on the additive color process, which arecolor-separated by, e.g., CCDs, is executed to determine whether or notthe input signals are those allowing image formation, and optimal colorreproduction can be realized according to the determination result.

For example, when it is determined that image formation is enabled, theinput image signals are converted into color image signals based on thesubtractive color process with reference to, e.g., a density conversiontable. Contrary to this, when it is determined that image formation ofthe input color image signals based on the additive color process isdifficult to perform, the input image signals are processed by, e.g.,conventional masking processing. In this manner, a processing system canbe selected in accordance with the distribution of colors of an originalon the color space coordinate system, and optimal color reproduction canbe realized according to originals.

Alternatively, the image processing apparatus comprises conversion meansfor respectively converting input color image signals into output colorimage signals by a plurality of kinds of methods, count means forchecking if the color image signals converted by the conversion meansfall within a reproduction range of an output apparatus, and countingthe number of pixels falling outside the reproduction range, andselection means for selecting the conversion means, corresponding to thesmallest count value of the count means, of the plurality of conversionmeans.

In the above arrangement, an optimal color image processing system canbe selected in accordance with the distribution of colors of the inputcolor image signals on a color space coordinate system, and optimalcolor reproduction can be realized in accordance with input color imagesignals.

Furthermore, a color image processing apparatus for processing inputcolor image signals, and recording/outputting the processed color imagesignals to an image output apparatus as a corresponding color image,comprises at least two kinds of signal processing means for executingcolor conversion processing by different methods, so that the inputcolor image signals can be output by the image output apparatus, storagemeans for storing chromaticity data within a color reproduction range,which can be recorded/output by the image output apparatus, comparisonmeans for comparing the chromaticity data stored in the storage meanswith chromaticity data of the input color image signals, calculationmeans for obtaining a value corresponding to a smallest color differencebetween the two chromaticity data upon comparison by the comparisonmeans in units of input color image signals, maximum value detectionmeans for detecting a maximum value of the color differences obtained bythe calculation means, and selection means for selecting an optimal oneof the signal processing means according to the maximum value detectedby the maximum value detection means.

In the above arrangement, the input color image signals arecolor-converted by the signal processing means selected by the selectionmeans, and the converted signals are output to the image outputapparatus as a corresponding recorded/output color image, so thatoptimal color conversion processing can be performed in accordance withan input image, and the best output can be obtained.

Moreover, a color image processing apparatus for converting input colorimage signals based on an additive color process into color imagesignals based on a corresponding subtractive color process, andoutputting the converted color signals to an output apparatus forprocessing the color signals, comprises conversion means for convertingthe input color image signals based on the additive color process intocolor image signals based on the corresponding subtractive color processby at least two methods, and outputting the converted image signals tothe output apparatus, color reproduction region storage means forstoring a color reproduction region on a color space of the outputapparatus, count means for checking if the input color image signalsfall within the color reproduction region of the output apparatus storedin the color reproduction region storage means in units of pixels, andcounting the number of pixels falling outside the color reproductionregion, determination means for determining whether or not the countvalue of the count means is equal to or smaller than a predeterminedthreshold value, and selection means for selecting an optimal one of theat least two conversion means in accordance with the determinationresult of the determination means, wherein the output apparatus canperform color reproduction equivalent to the input color image signals.

The output apparatus permanently visually presents a color image bymixing colors using toners or inks. The color reproduction regionstorage means stores the color reproduction region in which the inputcolor image signals are expressed by mixing colors using toners or inksof the output apparatus in a color space coordinate system. When theinput color image signals exceed the conversion color reproductionregion stored in the color reproduction region storage means, theselection means selects the conversion means which can perform optimalcompression for the input color image signals.

In the above arrangement, as an arrangement of a color reproductionprocessing system of a color image original, a color reproductionprocessing system for performing color reproduction color-matched with acolor image original only within the color reproduction region of theimage output apparatus is arranged in addition to a conventional colorspace compression mapping reproduction system. Thus, a processing systemcan be selected in accordance with the distribution of colors of anoriginal in the color space coordinate system upon reading of originals,and optimal color reproduction can be realized according to theoriginal,

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an arrangement of the first embodimentaccording to the present invention;

FIG. 2 is a block diagram showing the detailed arrangement of an imageinput apparatus of the first embodiment;

FIG. 3 is a block diagram showing an arrangement of the secondembodiment according to the present invention;

FIG. 4 is a chart showing a color reproduction region of an image outputapparatus in an L*a*b* uniform color space;

FIG. 5 is a block diagram showing an arrangement of the fifth embodimentaccording to the present invention;

FIG. 6 is a chart showing a determination region in a determinationtable on an a*-b* plane in the fifth embodiment;

FIG. 7 is a chart showing a color reproduction region of an image outputapparatus in an L*a*b* uniform color space in the fifth embodiment;

FIG. 8 is a block diagram showing an arrangement of the sixth embodimentaccording to the present invention;

FIG. 9 is a chart showing a color reproduction region of an image outputapparatus on an a*-b* plane, and the distances from the barycenter ofthe color reproduction region in the sixth embodiment;

FIG. 10 is a block diagram showing an arrangement of the seventhembodiment according to the present invention;

FIG. 11 is a schematic sectional view showing a structure of a colorcopying machine according to the eighth embodiment of the presentinvention;

FIG. 12 is a block diagram of an image processing unit of the eighthembodiment;

FIG. 13 is a graph showing density conversion curves used in the eighthembodiment;

FIG. 14 is a flow chart showing color conversion processing of theeighth embodiment;

FIG. 15 is a view showing sampled original image signals in the eighthembodiment;

FIG. 16 is a block diagram showing an arrangement of the ninthembodiment according to the present invention;

FIG. 17 is a flow chart showing color conversion processing of the ninthembodiment;

FIG. 18 is a block diagram showing an arrangement of the tenthembodiment according to the present invention;

FIG. 19 is a block diagram showing an arrangement of a conventionalcolor reproduction processing unit; and

FIG. 20 is a chart showing compression mapping of a color space by theconventional color reproduction processing.

FIG. 21 is a chart showing processing of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment according to the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment!

FIG. 1 is a block diagram showing an arrangement of an embodimentobtained when the present invention is applied to a color image copyingapparatus.

As shown in FIG. 1, the copying apparatus comprises three apparatuses,i.e., an image input apparatus 101 as an input unit of a color image, animage processing apparatus 102 for converting image input signals R(red), G (green) and B (blue) read by the image input apparatus 101 intoimage output signals, and an image output apparatus 103 for performing apermanent visual presentation corresponding to a plurality of colors oftoners or inks upon reception of the image output signals Y (yellow), M(magenta), C (cyan) and K (black) converted by the image processingapparatus 102.

Image signals processed by the image processing apparatus 102 are notlimited to those of a color image original or a printed matter read byan image reader comprising CCD sensor for R, G and B. For example, a CG(computer graphic) image output from a host computer, or an image pickedup by an electronic still camera can be similarly processed.

The image processing apparatus 102 comprises four gamma tables A to D(111 to 114), a color conversion look-up table 116, and an outputselection circuit 117. Note that the color conversion look-up table 116incorporates a code addition circuit 118 for adding a discriminationcode, and the output selection circuit 117 incorporates a count circuit119 for counting the number of "1"s of the discrimination code added bythe color conversion look-up table 116.

The image input apparatus 101 of this embodiment will be brieflydescribed below with reference to FIG. 2 for cases wherein a color imageis a printed original, and wherein a color image is a CG image.

A case will be exemplified below wherein the color image original is aprinted matter.

An original 202 placed on an original table glass 201 shown in FIG. 2 isilluminated with an original illumination halogen lamp 203, and isfocused on a CCD line sensor 205 by a rod lens array 204.

Red (R), green (G), and blue (B) color separation filters aredot-sequentially coated on the CCD line sensor 205. Thus, the sensor 205sequentially outputs R, G, and B color separation signals of an originalimage.

Reference numeral 206 denotes a sample & hold (S/H) circuit for samplingand holding outputs from the CCD line sensor 205 in units of pixels. Theoutputs from the S/H circuit 206 are converted into digital signals byan A/D converter 207.

Image data converted into the digital signals are input to a shadingcircuit 208 together with prestored (or previously obtained by readingwhite board before reading an image) white data (not shown). The outputnonuniformity of the image data due to a variation in sensitivity amongpixels corresponding to respective element of CCD is corrected, and thecorrected image data are standardized to a predetermined number of bits.

An input masking circuit 209 calculates the R, G, and B output signalsfrom the shading circuit 208 using a predetermined matrix, and outputsimage signals R', G', and B' standardized according to the NTSCstandards. ##EQU1##

The optimal solution of a matrix coefficient a_(ij) is determined by,e.g., the method what is called least squares.

A case will be described below wherein a color original image is a CGcolor image.

R, G, and B video signals output from a computer 210 are input to theinput masking circuit 209 via an interface 211. If these video signalscomply with the NTSC standards, the matrix coefficients of the inputmasking circuit go through. That is, the matrix coefficient is given by:##EQU2## The video signals are then output to the following imageprocessing apparatus 102.

The image processing apparatus 102 for converting the digital R, G, andB input signals into a plurality of colors of toner or ink outputsignals will be described in detail below.

R, G, and B image signals input from the image input apparatus 101 tothe image processing apparatus 102 are branched into n systems (n=4 inthis embodiment), and are input to n gamma tables which respectively hasdifferent characteristic (e.g., the gamma tables A (111) to D (114)).

Signals gamma-converted by the corresponding gamma tables are sent tothe color conversion look-up table 116, and are converted into Y, M, C,and K signals corresponding to the R, G, and B signals from the imageinput apparatus 101. The Y, M, C, and K signals are sent to the outputselection circuit 117.

Note that the color conversion look-up table 116 stores only data in thecolor reproduction region of the image output apparatus 103 on the colorspace of the L*a*b* colorimetric system. When the input R, G, and Bsignals fall within the color reproduction region of the image outputapparatus 103, the code addition circuit 118 adds a discrimination code"0" to the color-converted signals, and outputs these signals to theoutput selection circuit 117. However, when the input R, G, and Bsignals fall outside the color reproduction region of the image outputapparatus 103, the circuit 118 adds a discrimination code "1" to thecolor-converted signals, and outputs these signals to the outputselection circuit 117.

The count circuit 119 of the output selection circuit 117 counts thenumber of discrimination codes "1" to the color-converted signals of theinput n kinds of Y, M, C, and K output signals in units of gamma tables,and outputs the signals from a gamma table corresponding to the smallestnumber of discrimination codes "1" to the image output apparatus 103.

The count circuit 119 need not always count the number of discriminationcodes "1". For example, the circuit 119 may count the number ofdiscrimination codes "0", and the output selection circuit may outputsignals from a gamma table corresponding to the largest number ofdiscrimination codes "0" to the image output apparatus 103.

The image output apparatus 103 prints the image output signals (Y, M, C,and K) from the image processing apparatus 102 in correspondence with anoutput method such as a PWM method (multi-valued pixel output), a dithermethod, an error diffusion method (binary pixel output), or the like.

In the above embodiment, the color space distribution of a color imageoriginal is expressed using the L*a*b* uniform color coordinate system.However, the color space may be expressed using a color reproductionregion of the image output apparatus, which region is defined by an Luvcolorimetric system, an XYZ colorimetric system, or an RGB signalsystem, thus obtaining the same effect as described above.

It is effective to select an optimal gamma table in, e.g., a prescanmode.

More specifically, in a color copying machine, when an original isplaced on an original table, and a copy start key is depressed, aprescan operation prior to an actual printing operation is normallyexecuted so as to detect, e.g., an original size. In this case, theabove-mentioned algorithm is executed, so that the optimal processingsequence (selection of gamma table) can be executed in the main scanmode.

Foregoing processing is shown in FIG. 21.

An original is placed on an original table in step S101, and a copystart key is depressed at Step S102. In accordance with the ON of thecopy start key, an image reader including a CCD sensor starts relativedisplacement, and performs prescan in step S103. At this time,above-described counting by the count circuit 119 is performed in stepS104 as well as such process as detecting the original size andcontrolling exposure, and selection of the optimal gamma table fromamong gamma table 111 to 114 in step S105. Then, main scan is performedfor forming an image in step S106, and the image is output by an imageoutput apparatus 103 in step S107.

In the above described prescan, counting can be performed either at thetime of going or returning of the relative displacement.

Also, the prescan can be performed repeatedly.

By performing the prescan as described above, image memory for storingone frame of image data can be saved.

As described above, according to the above-mentioned embodiment, colorreproduction can be realized by performing optimal color conversionaccording to input color image signals.

More specifically, a plurality of kinds of gamma tables are prepared,and input signals are converted to fall within the color reproductionrange of the image output apparatus in accordance with an originalimage. Thus, when all the input signals fall within the colorreproduction range of the image output apparatus, unnecessarycompression is inhibited; otherwise, optimal compression can beperformed.

Especially in a grandchild copy, degradation of color reproducibilitycan be prevented as compared to a conventional apparatus.

Second Embodiment!

The second embodiment according to the present invention will bedescribed in detail below with reference to the accompanying drawings.

FIG. 3 is a block diagram showing an arrangement of a copying apparatusaccording to the second embodiment. In the second embodiment, thearrangements of the image input apparatus 101 and the image outputapparatus 103 are substantially the same as those in the firstembodiment, and a detailed description thereof will be omitted.

The detailed arrangement of an image processing apparatus 302 comprisingan arrangement different from that in the first embodiment will bedescribed below.

The image processing apparatus 302 of the second embodiment comprises acolor coordinate discrimination circuit 310, a density conversion table311, a density conversion circuit 312, a masking circuit 313, and aswitching circuit 314.

R, G, and B image signals input to the image processing apparatus 302are branched into two systems, i.e., inputs to the color coordinatediscrimination circuit 310, and inputs to the density conversion table311 (to be described later) and the density conversion circuit 312.

The color coordinate discrimination circuit 310 discriminates whetherthe distribution of a color image original on the color space isincluded in the color reproduction region of the image output apparatus103 or exceeds it by a method to be described below.

R, G, and B image signals input to the color coordinate discriminationcircuit 310 are converted into tristimulus values X, Y, and Z of the XYZcolorimetric system.

When the R, G, and B signals comply with the NTSC scheme, a conversionformula is given by: ##EQU3##

The image signals converted into the tristimulus values X, Y, and Z arethen converted into L*, a*, and b* of the L*a*b* colorimetric system.##EQU4##

FIG. 4 shows a state on the L*a*b* colorimetric system. A hexahedronindicated by solid lines in FIG. 4 represents the color reproductionregion of the image output apparatus 103 described above. When imagesignals are present in this hexahedron, the image output apparatus canreproduce colors.

Whether or not the image signals converted into the L*a*b* coordinatesby equation (2) fall within the color reproduction region is determinedin units of pixels by the following method.

The color coordinate discrimination circuit 310 comprises a color memory310a comprising ROM, RAM and so on for storing color information of aregular hexahedron (a solid indicated by alternate long and short dashedlines in FIG. 4) inscribing the hexahedron of the reproduction region,and data achromatic color data) near a straight line connecting K and Win FIG. 4.

The data in the color memory 310a are looked up in units of pixels ofthe image signals converted into the L*a*b* coordinates by equation (2),and the number of pixels falling outside the regular hexahedron iscounted. Whether or not the count value exceeds a given threshold valueis determined to check whether or not colors of an original fall withinthe color reproduction region of the image output apparatus 103, therebyoutputting a 1-bit discrimination signal.

For example, when a color image original is an output image of thecopying apparatus of this embodiment (to be referred to as a "generationcopy" or a "grandchild copy" hereinafter), all the image data arepresent within the color reproduction region, and the color coordinatediscrimination circuit 310 always discriminates that all the pixels arepresent in the reproduction region.

Of the R, G, and B image signals input to the image processing apparatus302, the other branched system is further branched into two systems. Onesystem is subjected to the same processing as that executed by the logconversion circuit 402 and the masking circuit 403 in the prior artshown in FIG. 19 by the density conversion circuit 312 and the maskingcircuit 313.

More specifically, the color space of a color image original is set tobe larger than the color reproduction region of the image outputapparatus 103, and is reproduced while being compressed, therebyexecuting processing for outputting an image having a gradationcharacteristic for color coordinates falling outside the colorreproduction region.

Meanwhile, the image signals are also input to the density conversiontable 311 simultaneously with the above-mentioned color processing. Thedensity conversion table 311 is a conversion table for receiving the R,G, and B image signals, and outputting Y, M, C, and K output signals.

A method of creating the density conversion table 311 will be brieflydescribed below.

It is assumed to be already known that reproduction colors obtained whena given set (y, m, c, k) of Y, M, C, and K output signals are printed bythe image output apparatus 103 are (l*,a*,b*) on the L*a*b* coordinatesystem.

On the other hand, the L*, a*, and b* coordinates of R, G, and B imageread signals can be calculated by equations (1) and (2). Therefore, theR, G, and B image read signals can colorimetrically correspond to Y, M,C, and K output signals via the L*a*b* coordinate system.

In general, in an image recording apparatus for printing an image usingfour colors Y, M, C, and K, a reproduction color printed based on agiven set of output signals (Y₁, M₁, C₁, K₁) is often colorimetricallycolor-matched with that printed based on another set of output signals(Y₂, M₂, C₂, K₂).

This is because black defined by mixing three colors Y, M, and C iscolor-matched with black defined by K. This means that different sets ofY, M, C, and K output values are present in correspondence with a set ofmixing color coordinates (l*,a*,b*).

In this table, of a plurality of sets of Y, M, C, and K output values,which sets are color-matched with each other, a set having the largest Ksignal is determined as an output value. This is to enhance the effectof UCR (undercolor removal) processing.

The conversion table created as described above allows colorreproduction color-matched with a color image original within the colorreproduction region.

Of the image output signals (Y₁, M₁, C₁, K₁) and (Y₂, M₂, C₂, K₂)converted in the respective systems, when it is determined based on thediscrimination result of the color coordinate discrimination circuit 310that the color image original exceeds the color reproduction region, theswitching circuit 314 selects the output signals (Y₁, M₁, C₁, K₁)obtained by compressed color processing. On the other hand, when it isdetermined that the color image original falls within the colorreproduction region, the switching circuit 314 selects the outputsignals (Y₂, M₂, C₂, K₂) obtained by the color-matched colorreproduction processing. In either case, the selected output signals areoutput to the image output apparatus 103.

In the second embodiment described above, the color space distributionof a color image original is discriminated by the color coordinatediscrimination circuit 310. In this case, data stored in the colormemory 310a define a maximum regular hexahedron in the colorreproduction region of the image output apparatus for the purpose ofdecreasing the number of bits. However, the present invention is notlimited to the above embodiment. For example, the data may include allthe signal values in the color reproduction region, thus allowing moreprecise discrimination.

In the second embodiment, the color space of the color coordinatediscrimination circuit 310 is expressed using the L*a*b* uniform colorcoordinate system. However, the color space of the color coordinatediscrimination circuit 310 may be expressed by a color reproductionregion of an image output apparatus, which region is defined by an Luvcolorimetric system, an XYZ colorimetric system, or an RGB signalsystem, thus obtaining the same effect as described above.

It is effective to perform the above-mentioned discrimination in theprescan mode like in the first embodiment.

In the above description, when the color space distribution of a colorimage original exceeds the color reproduction region, calculationprocessing by the density conversion circuit 312 and the masking circuit313 is executed. Alternatively, a correspondence between input andoutput signals of this processing system may be calculated beforehand,and may be written in a look-up table (ROM, RAM and so on) so as toexecute color reproduction processing of a compressed space.

Furthermore, the correspondence between input and output signals to bewritten in a look-up table may be a relation other than by calculationof approximate equation.

As described above, according to the second embodiment, the color spacedistribution of a color image original is detected to check if the colorspace distribution is present within the color reproduction region. Oneof outputs from different color processing systems is then selectedaccording to the original. In this manner, color reproduction that canmaintain a gradation characteristic of a color image original exceedingthe color reproduction region of the image output apparatus, or colorreproduction faithful to a color image original within the colorreproduction region, can be performed, and an optimal output image canbe obtained.

An image free from a change in reproduction color can be obtained forrepetitive grandchild copies.

As described above, according to the present embodiment, as thearrangement of the color reproduction processing system of a color imageoriginal, a color reproduction processing system for performing colorreproduction color-matched with an input color image only within thecolor reproduction region of the image output apparatus is arranged inaddition to the conventional color space compression mappingreproduction system. Therefore, a processing system can be selected inaccordance with the spread of colors of input color image signals on thecolor space coordinate system, and optimal color reproduction can berealized in accordance with an input color image.

More specifically, as the arrangement of the color reproductionprocessing system of a color image original, a color reproductionprocessing system for performing color reproduction color-matched withan input color image only within the color reproduction region of theimage output apparatus is arranged in addition to the conventional colorspace compression mapping reproduction system. Therefore, a processingsystem can be selected in accordance with the spread of colors of inputcolor image signals on the color space coordinate system, and optimalcolor reproduction can be realized in accordance with an input colorimage.

Third Embodiment!

The third embodiment according to the present invention will bedescribed in detail below with reference to the accompanying drawings.

The hardware arrangement of the third embodiment is the same as that ofthe second embodiment described above. A difference from the secondembodiment is that the color coordinate discrimination circuit 310 doesnot incorporate the color memory 310a for determining based on a look-upresult of the storage data in the color memory 310a whether or notcolors of an original fall within the color reproduction region of theimage output apparatus 103, but performs discrimination as follows.

Discrimination processing for determining whether or not colors of anoriginal fall within the color reproduction region according to thethird embodiment will be explained below.

In the third embodiment, whether or not image signals converted into theL*a*b* coordinates by equation (2) fall within the color reproductionregion is checked in units of pixels by the following method.

An equation for each plane of the hexahedron as the color reproductionregion of the image output apparatus 103 in the above-mentioned L*a*b*colorimetric system shown in FIG. 4 is given by: ##EQU5## Therefore, inthe hexahedron, image signals (L*,a*,b*) must satisfy the followingrelation for each plane: ##EQU6##

In this manner, the above-mentioned discrimination is performed in unitsof pixels for the entire surface or a portion of a color image original,and the number of pixels present within the color reproduction region isaccumulated.

Upon completion of the above-mentioned processing for a predeterminedregion, the accumulated value is compared with a predetermined thresholdvalue. For example, when 95% or more of an original image are present inthe color reproduction region, it is determined that the color spacedistribution of the color image original is present within the colorreproduction region, and a 1-bit discrimination signal is output.

In the third embodiment described above, the color space distribution ofa color image original is automatically discriminated by the colorcoordinate discrimination circuit 310. For example, when a user caneasily determine the color space distribution of an original image likein a case wherein an output image from the apparatus of this embodimentis used as an original (grandchild copy), the output from the switchingcircuit 314 may be switched in accordance with an operation inputinstruction from an operation unit (not shown) of the apparatus of thisembodiment, thus obtaining the same effect as described above.

In the third embodiment, the color space of the color coordinatediscrimination circuit 310 is expressed using the L*a*b* uniform colorcoordinate system. However, the color space of the color coordinatediscrimination circuit 310 may be expressed by a color reproductionregion of an image output apparatus, which region is defined by an Luvcolorimetric system, an XYZ colorimetric system, or an RGB signalsystem, thus obtaining the same effect as described above.

In the second and third embodiments described above, whether or notcolors of an original are present within the color reproduction regionis discriminated by the color coordinate discrimination circuit 310.Alternatively, the color space may be divided into small color spaceblocks, and to which small color space blocks an original image belongsmay be accumulated in units of blocks. Then, the number of blocks wherethe colors of an original image are present, and coordinates of theblocks on the color space may be discriminated to discriminate the colorspace distribution of the original image.

Two color reproduction processing systems, i.e., a compressionreproduction system and a color-matching reproduction system on thecolor space are presented. In addition, a color processing system forperforming enlargement on the color space may improve a gradationcharacteristic.

This example will be briefly described below. Assume a map as a colorimage original to be color-copied. In most maps, the depths of seas areexpressed by changing the density from white to blue or cyan. Theheights of mountains are expressed by changing the density from yellowto brown.

When original image colors are distributed on small regions in the colorspace in this manner, optimal color reproduction on visual recognitioncan be realized by performing enlarged reproduction on the color space(e.g., increasing the saturation on the color space).

As described above, according to the present invention, as thearrangement of the color reproduction processing system of a color imageoriginal, a color reproduction processing system for performing colorreproduction color-matched with an input color image only within thecolor reproduction region of the image output apparatus is arranged inaddition to the conventional color space compression mappingreproduction system. Therefore, a processing system can be selected inaccordance with the spread of colors of input color image signals on thecolor space coordinate system, and optimal color reproduction can berealized in accordance with an input color image.

In this case, whether or not input color image signals fall within thecolor reproduction region of the image output apparatus can be easilydiscriminated by only simple calculation processing without arranging,e.g., a color memory.

Furthermore, for a color image original distributed on small regions inthe color reproduction region, a gradation characteristic can beprovided to an original, and an optimal output image in terms of goodvisual recognition can be obtained.

Fourth Embodiment!

In the above description, when the color space distribution of a colorimage original is included in the color reproduction region, signalconversion based on table conversion using the density conversion table311 is executed. Alternatively, color reproduction by a nonlinearmasking calculation including higher-order terms than one-order may beperformed without using a table.

In masking used in this case, for example, coefficients a_(i),j aredetermined by, e.g., the method of least squares by samplingrepresentative colors in the color reproduction region using thefollowing matrix: ##EQU7##

In this manner, density conversion can be performed without arrangingtables or the like.

In each of the above-mentioned embodiments, input signals to the densityconversion tables are R, G, and B signals complying with the NTSCscheme. Alternatively, L*, a*, and b* signals generated by the colorspace coordinate discrimination circuit 310 may be used as input imagesignals to the density conversion table. In this case, image inputsignals input to the image input apparatus 101 through, e.g., an I/F arenot limited to R, G, and B color-separation signals, and if physicalamounts L*, a*, and b* on the L*a*b* uniform color coordinate system arecolorimetrically known, color reproduction is enabled.

As described above, according to the above embodiment, the color spacedistribution of a color image original is detected to check if the colorspace distribution is present in the color reproduction range, and oneof outputs from different color processing systems is selected accordingto an original. Thus, color reproduction that can maintain a gradationcharacteristic of a color image original exceeding the colorreproduction region of the image output apparatus, or color reproductionfaithful to a color image original within the color reproduction region,can be performed, and an optimal output image can be obtained.

An image free from a change in reproduction color can be obtained forgrandchild copies.

Fifth Embodiment!

The fifth embodiment according to the present invention will bedescribed in detail below with reference to the accompanying drawings.

FIG. 5 is a block diagram showing an arrangement of a copying apparatusaccording to the fifth embodiment of the present invention.

The same reference numerals in FIG. 5 denote the same parts as in FIGS.1 and 2, and a detailed description thereof will be omitted.

As shown in FIG. 5, the copying apparatus of this embodiment comprisesthree apparatuses, i.e., an image input apparatus 501 as a color imageinput unit, an image processing apparatus 502 for converting image inputsignals read by the image input apparatus 501 into image output signals,and an image output apparatus 503 for performing a permanent visualpresentation corresponding to a plurality of colors of toners or inksupon reception of the image output signals converted by the imageprocessing apparatus 502.

The image processing apparatus 502 comprises a switching circuit 512, alog conversion circuit 513, a masking circuit 514, a discriminationtable 515, a calculation circuit 516, and a selection circuit 517.

The image input apparatus 501 comprises only an original reading unit ascompared to the first embodiment, and control for reading a color imageoriginal is the same as that in the first embodiment shown in FIG. 2.

The image processing apparatus 502 for converting digital R, G, and Binput signals into a plurality of colors of ink or toner output signalsaccording to this embodiment will be described in detail below.

In the apparatus of this embodiment, prior to a copying operation of anoriginal, the color space region of an original is discriminated by aprescan operation of the image input apparatus 501. For this purpose, R,G, and B image signals input to the image processing apparatus 502 areselectively output to the discrimination table 515 side by the switchingcircuit 512.

The discrimination table 515 discriminates using the above-mentionedconversion equations (1) and (2) like in the color coordinatediscrimination circuit 310 of the above embodiments whether or not thedistribution of a color image original on the color space is included inthe color reproduction region of the image output apparatus 103.

FIG. 6 shows a discrimination region of the discrimination table 515 onan a*-b* plane in the L*a*b* colorimetric system. A region A in FIG. 6represents the color reproduction region of the image output apparatus103.

The color space is divided into a region B obtained by slightly wideningthe color reproduction region A, a region C obtained by slightlywidening the region B, and the remaining region D.

FIG. 7 shows a state of the color space of the color reproduction regionA of the image output apparatus 103 on the L*a*b* colorimetric system.

The discrimination table 515 outputs a 2-bit signal indicating one ofthe regions A to D in accordance with upper 5 bits of each of the R, G,and B signals

The discrimination signal output from the discrimination table 515 isinput to the calculation circuit 516. The calculation circuit 516calculates the sum of pixels corresponding to the regions A to D. Theselection circuit 117 sets optimal masking coefficients on the basis ofthe calculation result. For example, selection criterions are set asfollows. ##EQU8##

The optimal parameters are set in this manner.

Upon completion of setting of the parameters, the main scan operation ofthe image input apparatus 501 is started, and color conversionprocessing is executed based on the parameters selected in the prescanoperation, thereby copying an image.

When an image is to be copied, R, G, and B image signals input to theimage processing apparatus 502 are input to the log conversion circuit513 side by the switching circuit 512, and are converted intocorresponding C, M, and Y image signals by the log conversion circuit513.

The C, M, and Y image signals are then input to the masking circuit 514,and are subjected to the masking calculation using the optimalcoefficients based on the discrimination result.

In this manner, both color reproduction and gradation expression can besatisfactorily maintained.

The image output apparatus 103 prints the image output signals (Y, M, C,K) in correspondence with an output method such as a PMM method, adither method, an error diffusion method, or the like.

As described above, according to this embodiment, the color spacedistribution of a color image original is detected, and processing isexecuted using parameters which can minimize compression in the colorspace, so that color reproduction faithful to colors of an original, andfree from degradation of a gradation characteristic can be performed.

An image free from a change in reproduction color can be obtained forrepetitive grandchild copies.

In the fifth embodiment described above, the color space distribution ofa color original is automatically discriminated by the discriminationtable 515. For example, when a user can easily determine the color spacedistribution of an original image like in a case wherein an output imageof the copying apparatus of this embodiment is used as an original(grandchild copy), the selection circuit 517 may be switched in responseto an instruction input from an operation unit of the copying apparatusof this embodiment, thus obtaining the same effect as described above.

Sixth Embodiment!

In the above description, the masking coefficients are changed inaccordance with the color space distribution of an original. In place ofthe color space distribution of an original, image signals obtained byreading an original are converted into a predetermined color spacecoordinate system, and masking coefficients may be changed in accordancewith the distance between the converted coordinate position and thecentral coordinate position of the color reproduction region, which canbe output by the image output apparatus, thus obtaining the same effectas described above.

FIG. 8 shows the arrangement of the sixth embodiment according to thepresent invention. The same reference numerals in FIG. 8 denote the sameparts as in the fifth embodiment shown in FIG. 5, and a detaileddescription thereof will be omitted. In FIG. 8, an image processingapparatus 602 is different from that in the fifth embodiment shown inFIG. 5.

In FIG. 8, a color coordinate conversion circuit 615 for convertingimage signals obtained by reading an original into a predetermined colorspace coordinate system is arranged in place of the discrimination table515 shown in FIG. 5. In addition, a calculation circuit 616 forcalculating the distance between the converted coordinate position ofimage signals converted into the color space coordinate system by thecolor coordinate conversion circuit 615, and the central coordinateposition of the color reproduction region, which can be output by animage output apparatus 103, is arranged.

R, G, and B image signals input to the image processing apparatus 602 bya prescan operation of an image input apparatus 501 are selectivelyoutput to the color coordinate conversion circuit 615 side by aswitching circuit 512. This is to convert image signals obtained byreading an original into the color space coordinate system, and tochange masking coefficients in accordance with the distance between theconverted coordinate position and the central coordinate position of thecolor reproduction region, which can be output by the image outputapparatus 103.

Like in the color coordinate discrimination circuit 310 described above,the color coordinate conversion circuit 615 discriminates, by a methodto be described below, whether the distribution of a color imageoriginal on the color space is included in or exceeds the colorreproduction region of the image output apparatus 103.

R, G, and B image signals input to the color coordinate conversioncircuit 615 are converted into tristimulus values X, Y, and Z of the XYZcolorimetric system. When the R, G, and B signals comply with the NTSCscheme, the conversion equation is expressed by equation (1) of thefirst embodiment.

The image signals converted into the tristimulus values X, Y, and Z byequation (1) are converted into L*, a*, and b* signals of the L*a*b*colorimetric system by the above-mentioned equation (2).

The image signals converted into the L*, a*, and b* coordinates byequation (2) are input to the calculation circuit 616 so as to obtainthe distance from the barycenter (L₀, a₀, b₀) of the color reproductionregion of the image output apparatus 103.

The distance r is obtained by the following equation (3):

    r=(L*-L.sub.0).sup.2 +(a*-a.sub.0).sup.2 +(b*-b.sub.0).sup.2(3)

FIG. 9 shows a state on the L*a*b* colorimetric system. A hexagonindicated by solid lines in FIG. 9 represents the color reproductionregion of the image output apparatus 103 described above. When imagesignals are present in this hexagon, the image output apparatus canreproduce colors.

To which regions A to D shown in FIG. 9 the input image signals belongis determined in accordance with the obtained distance r, and the numberof pixels belonging to the regions A to D is counted in units ofregions.

A selection circuit 517 selects optimal masking coefficients inaccordance with the count result, and sets the selected coefficients ina masking circuit 514.

The selection criterions are the same as those used when the calculationcircuit 516 in the fifth embodiment described above calculates the sumof pixels belonging to the regions A to D, and the selection circuit 517sets optimal masking coefficients based on the calculation result.

Upon completion of setting of the parameters, the main scan operation ofthe image input apparatus 501 is started, and color conversionprocessing is executed based on the parameters selected in the prescanoperation, thereby copying an image.

As described above, according to this embodiment, the color spacedistribution of a color image original is detected, and processing isexecuted using parameters which can minimize compression in the colorspace, so that color reproduction faithful to colors of an original, andfree from degradation of a gradation characteristic can be performed.

An image free from a change in reproduction color can be obtained forrepetitive grandchild copies.

In the fifth and sixth embodiments described above, the maskingcoefficients are changed in accordance with the color distribution of anoriginal. A plurality of sets of R→C, G→M, and B→Y conversion tables maybe prepared, and may be selected in accordance with the colordistribution, thus allowing gradation expression faithful to anoriginal.

As described above, according to the present invention, a processingsystem can be selected in accordance with the spread of colors of inputcolor image signals on the color space coordinate system, and optimalcolor reproduction can be realized according to an input color image.

In addition, an image free from a change in reproduction color can beobtained for repetitive grandchild copies.

Seventh Embodiment!

The seventh embodiment according to the present invention will bedescribed in detail below with reference to the accompanying drawings.

FIG. 10 is a block diagram showing an arrangement of an embodimentwherein the present invention is applied to a copying apparatus.

As shown in FIG. 10, the copying apparatus of this embodiment comprisesthree units, i.e., an input apparatus including a sensor unit A forreading a color image, an illumination lamp 1003, and the like, an imageprocessing unit for converting the image input signals read by the inputapparatus into image output signals, and an image forming unit 1020 forperforming a permanent visual presentation corresponding to a pluralityof colors of toners or inks upon reception of the image output signalsconverted by the image processing unit.

Note that FIG. 10 illustrates only the input apparatus as a means forinputting image signals. However, image signals to be processed by theimage processing unit are not limited to a color image original or aprinted matter read by the input apparatus. For example, a CG (computergraphic) image, an image picked up by an electronic still camera, andthe like can be similarly processed.

The image processing unit comprises the following arrangement.

More specifically, reference numeral 1006 denotes a sample & hold (S/H)circuit for sampling and holding outputs from a CCD sensor 1005 in unitsof pixels. Reference numeral 1007 denotes an A/D converter; and 1008, ashading circuit for correcting an output nonuniformity caused by avariation in sensitivity among pixels of the CCD sensor 1005, andstandardizing inputs to a predetermined number of bits. Referencenumeral 1009 denotes a look-up table. The look-up table 1009 includes atable 1014 for storing data for determining whether or not outputsignals Y, M, C, and K corresponding to input signals R, G, and B are acombination of signals within a color reproduction range obtained bymixing colors of inks or toners by the image forming unit 1020.

Reference numeral 1010 denotes a log conversion circuit similar to thelog conversion circuit 402 shown in FIG. 19; 1011, a masking circuitsimilar to the masking circuit 403 shown in FIG. 19; 1012, a switchingcircuit for selecting signals from the masking circuit 1011 or signalsfrom a density conversion table 1013, and sending the selected signalsto the image forming unit; and 1013, the density conversion table forconverting R, G, and B signals into corresponding Y, M, C, and Ksignals. Reference numeral 1015 denotes a selection circuit forindicating inputs to be selected to the switching circuit 1012 accordingto the sign of the output from the look-up table 1009.

The operation of the seventh embodiment with the above arrangement willbe described hereinafter.

When a copy start button (not shown) is depressed, an original 1001 onan original table glass 1002 is illuminated with the illumination system1003. In correspondence with this operation, the sensor unit A(comprising a lens system 1004 including, e.g., a short focus lensarray, and a sensor 5100) is moved in a direction of an arrow v so as toperform a prescan operation, thereby sampling image information on theoriginal.

Red (R), green (G), and blue (B) color separation filters aredot-sequentially coated on the CCD sensor 1005. Thus, the sensor 1005sequentially outputs R, G, and B color separation signals of an originalimage.

Outputs from the CCD sensor 1005 are analog signals. These analogsignals are input to the S/H circuit 1006, and are sampled and held inunits of pixels. Thereafter, the analog signals are converted intocorresponding digital signals by the A/D converter 1007. Image dataconverted into the digital signals by the A/D converter 1007 are inputto the shading circuit 1008 together with prestored white data (notshown). The output nonuniformity of the image data due to a variation insensitivity among pixels of the CCD sensor 1005 is corrected, and thecorrected image data are standardized to a predetermined number of bits.

When it is determined by the table 1014 of the look-up table 1009 that acombination of the input image signals R, G, and B falls within thecolor reproduction range of the image forming unit 1020, the sign (+) ofthe output from the look-up table 1009 is set. On the other hand, whenthe combination of the input image signals R, G, and B falls outside thecolor reproduction range of the image forming unit 1020, the sign (-) ofthe output from the look-up table 1009 is set.

When the output from the look-up table 1009 has the sign (+), theselection circuit 1015 selects the density conversion table 1013, andsends the R, G, and B signals to the density conversion table 1013.Thus, the density conversion table 1013 converts the R, G, and B signalBinto the corresponding Y, M, C, and K signals .

The selection circuit then controls the switching circuit 1012 to sendsignals from the density conversion table 1013 to the image forming unit1020. The image forming unit 1020 executes a known image formingprocess, thereby permanently visually presenting a color imagecorresponding to the input color image signals. For this reason, colorreproduction of the output image is substantially equal to the readoriginal in this case.

For example, when a color image original is an output image of thecopying apparatus of this embodiment, all the image data are present inthe color reproduction region, and the output from the look-up table1009 has the sign (+).

On the other hand, when the output from the look-up table 1009 has thesign (-), the selection circuit 1015 selects the log conversion circuit1010 and the masking circuit 1011, and sends the R, G, and B signals tothe log conversion circuit 1010. Thus, known color conversion processingis executed to output an image having a gradation characteristic forcolor coordinates falling outside the color reproduction region.

The selection circuit instructs the switching circuit 1012 to select thesignals from the masking circuit 1011, and also controls the switchingcircuit 1012 to send the signals from the masking circuit 1011 to theimage forming unit 1020. The image forming unit 1020 executes a knownimage forming process, thereby permanently visually presenting a colorimage corresponding to the input color image signals.

In this manner, even when an input original has color coordinatesoutside the color reproduction region of the image forming unit 1020, animage having a gradation characteristic can be output.

In the above description, the color conversion processing is selected inaccordance with the sign of the output from the look-up table 1009.However, the present invention is not limited to the above embodiment.For example, when the output from the look-up table 1009 has the sign(-), the number of pixels having the sign (-) may be counted by theselection circuit 1015 to make the following control in place ofimmediately selecting the log conversion circuit 1010 and the maskingcircuit 1011. That is, when the probability of pixels having the sign(-) in the entire original is 5% or higher, the log conversion circuit1010 and the masking circuit 1011 may be selected to select the samecolor processing method as in the conventional apparatus. On the otherhand, when the probability is 5% or less, conversion (direct densityconversion) for directly obtaining density signals using the look-uptable 1009 and the density conversion table 1013 may be performed. Inthis case, the threshold value is not limited to 5%. An arbitrarythreshold value allowing good color reproducibility can be selectedaccording to the processing result.

As described above, according to this embodiment, the look-up table 1009for determining whether or not input color-separation signals R, G, andB fall within a color reproduction range defined by mixing colors ofinks or toners of the image forming unit 1020, is arranged, and the nextprocessing is switched according to the determination result, therebysolving the conventional problems in that the gradation characteristicof an image including only signals allowing color reproduction isimpaired or colors of the image are changed by compressing the image bymasking for providing the gradation characteristic. Thus, an imageallowing color reproduction can be directly subjected to densityconversion by switching a density conversion method, and the gradationcharacteristic can be prevented from being impaired.

As described above, according to the present invention, colorreproduction that can maintain a gradation characteristic of a colorimage original exceeding the color reproduction region of an imageoutput apparatus, or color reproduction faithful to a color imageoriginal within the color reproduction region, can be performed, and anoptimal output image can be obtained.

An image free from a change in reproduction color can be obtained forrepetitive grandchild copies.

Eighth Embodiment!

The eighth embodiment according to the present invention will bedescribed in detail below with reference to the accompanying drawings.

In the following description, the present invention is applied to acolor copying apparatus.

FIG. 11 is a schematic sectional view showing the structure of the colorcopying apparatus according to the embodiment of the present invention,and FIG. 12 is a block diagram of an image processing unit of thisembodiment.

In FIG. 11, reference numeral 1110 denotes an original readingapparatus; and 1106, an output apparatus (print engine).

The original reading apparatus 1110 outputs color image signals based onthe additive color process, expressed by three primary colors, i.e., red(R), green (G), and blue (B), to an image processing unit (to bedescribed later). The output apparatus 1106 receives color image signalsbased on the subtractive color process, expressed by three primarycolors, i.e., yellow (Y), magenta (M), and cyan (C), or four colorsobtained by adding black (K) to the three primary colors from the imageprocessing unit of this embodiment, and prints out these image signals.

An original 1101 is placed on an original table glass 1111, and isilluminated with illumination light from an illumination device 1112 ofan optical system unit 1115. Light reflected by the original 1101 isfocused on a color photoelectric transducer array 1102 via a short-focuslens array 1113. The optical system unit 1115 is moved in a direction ofan arrow in FIG. 11 to scan the original 1101 from the left to the rightin FIG. 11, thereby reading the original 1101.

An original image read in this manner is converted into electricalsignals by the color photoelectric transducer array 1102 (also shown inFIG. 12). The electrical signals are subjected to predetermined colorconversion processing in the image processing unit (FIG. 12).Thereafter, the processed signals are printed out by a print engine1106.

In the print engine 1106, a laser 1125 is driven to emit light inaccordance with the color image signals (Y, M, C, and K) color-convertedby the image processing unit. Light emitted from the laser 1125 isscanned on a photosensitive drum 1119 by a polygonal mirror 1116, whichis rotated at high speed. Thus, an electrostatic latent imagecorresponding to the laser drive signal is formed on the photosensitivedrum 1119. Note that the photosensitive drum 1119 is charged in advanceby a charger 1120 before a latent image is formed thereon.

The photosensitive drum 1119 is rotated in a direction of an arrow inFIG. 11, and is developed by a rotary developing unit 1122. Parallel tothis operation, a recording sheet 1123 fed from a paper feed cassette1114 is wound around a transfer drum 1118. An image in the first coloris transferred from the developed photosensitive drum 1119 to the blanksheet wound around the transfer drum 1118. Upon completion of thetransfer operation, the rotary developing unit is rotated by a 1/4revolution, and transfer operations of a total of four colors areexecuted. The recording sheet on which images are transferred, is fixedby fixing rollers 117, and is exhausted.

In this manner, a hard copy corresponding to the read original 1101 isobtained.

The arrangement of the print engine 1106 is substantially the same asthat of the image output apparatus 103, a detailed description of whichis omitted in the above embodiments.

A color conversion processing unit of this embodiment with the abovearrangement will be described below with reference to FIG. 12.

In FIG. 12, the same reference numerals denote the same parts as in FIG.11, and a detailed description thereof will be omitted.

In FIG. 12, reference numeral 1103 denotes an A/D converter forconverting analog electrical signals from the color photoelectrictransducer array 1102 into corresponding digital signals; 1104, adensity converter for performing density conversion processing of inputcolor image signals; and 1105, a masking•UCR circuit.

In the density converter 1104 of this embodiment, a plurality of curvetables (e.g., 1 to 4 are prepared, as shown in FIG. 13.

In the masking•UCR circuit 1105, a plurality of sets of maskingcoefficients corresponding in number to the curve tables are prepared.Note that masking coefficients mean, e.g., a 3×3 matrix, and a total ofnine coefficients form one set.

Reference numeral 1108 denotes a RAM for temporarily storing digitalimage signals; 1109, a CPU for controlling the overall apparatus of thisembodiment according to a control sequence (FIG. 14; to be describedlater) stored in a ROM 1124; and 1124, the ROM for storing theabove-mentioned program, a color space which can be output by the printengine 1106, and the like.

The color space which can be output by the print engine 1106 is obtainedby storing colors of hard copies as L*, a*, and b* values obtained byinputting various combinations of Y (yellow), M (magenta), C (cyan), andK (black) signals to the print engine 1106. The color space representsL'*_(i), a'*_(i), and b'*_(i) values (i is the color number of a hardcopy) falling within the color reproduction region of the print engine1106.

In this embodiment, input digital image signals are not limited to imagesignals from the reading apparatus 1110. For example, image signals froman external input apparatus 1130 can be input, and can be printed out bythe print engine 1106 as a corresponding image. In this case, the inputimage signals from the external input apparatus 1130 or outputs from theA/D converter 1103 are selected, and the selected inputs are input tothe density converter 1104 or the RAM 1108.

Note that the external input apparatus 1130 comprises, e.g., a computer,an SV (still video) camera, a video apparatus, or the like.

Color conversion processing of the apparatus of this embodiment with theabove arrangement will be described below with reference to the flowchart shown in FIG. 14.

In step S1, the original 1101 is read by the original reading apparatus1110. The read original color image based on the additive color process,expressed by three primary colors, i.e., red (R), green (G), and blue(B), is converted into corresponding analog electrical signals by thecolor photoelectric transducer array 1102. The analog signals aresupplied to the A/D converter 1103. The A/D converter 1103 converts theanalog signals from the color photoelectric transducer array 1102 intocorresponding digital signals. For this reason, the CPU 1109 samplessome input color image signals, and temporarily saves them in the RAM1108 in step S2.

For example, as shown in FIG. 15, components indicated by ◯ of the inputcolor image signals are sampled, and are saved in the RAM 1108.

In step S3, the CPU 1109 calculates and discriminates the saved imagesignals. More specifically, the CPU executes the following procedure.

R, G, and B image signals are converted into L*, a*, and b* signals. TheL*, a*, and b* signals represent a uniform color space (determined bythe CIE in 1976).

The values are represented by L*_(j), a*_(i), and b*_(j) (j is thesampling number). Then, a minimum difference ΔE between L'*_(i),a'*_(i), and b'*_(i) values (i is the color number of a hard copy), andL*, a*, and b* values obtained by sampling and converting the imagesignals is obtained for each image signal j:

    ΔE.sup.2.sub.j =(L*.sub.j -L'*.sub.i).sup.2 +(a*.sub.j -a'*.sub.i).sup.2 +(b*.sub.j -b'*.sub.i).sup.2

In step S4, a maximum one of the differences ΔE_(j) obtained in step S3is obtained, and is represented by ΔE_(max).

In step S5, the area of the actual color space as compared to the colorspace which can be output by the print engine is discriminated based onΔE_(max) and an optimal curve table is selected from the densityconversion table shown in FIG. 13 on the basis of the discriminationresult. More specifically, when ΔE_(max) is small, the curve table 4 isselected, and as ΔE_(max) becomes smaller, the tables 3, 2, and 1 areselected in turn.

The selected curve table is set in the density converter 1104. At thesame time, a plurality of sets of masking coefficients corresponding innumber to the curve table set in the density converter 1104 are set inthe masking•UCR circuit 1105, so that color conversion processing isexecuted by a plurality of kinds of processing methods.

In this manner, upon completion of selection of the color conversionprocessing corresponding to the image signals sampled and saved in theRAM 1108, the original reading apparatus 1110 begins to read theoriginal again in step S6. The read image is subjected to the selectedcolor conversion processing, and is output to the print engine 1106,thus obtaining a hard copy.

More specifically, an image read by the photoelectric transducer array1102 shown in FIG. 11 is converted into corresponding digital signals bythe A/D converter 1103. R (red), G (green), and B (blue) color signalsare color-converted into C, M, and Y color signals in accordance withthe curve table set in the density converter 1104, and the C, M, and Ysignals are converted into Y (yellow), M (magenta), C (cyan), and K(black) signals by removing color muddiness by the masking•UCR circuit1105. The color-converted color image signals are supplied to the printengine 1106, and a color hard copy 1107 is obtained.

As described above, according to this embodiment, the number of colorsof input signals, and the number of post-processing colors are counted,and color conversion processing having the smallest difference betweenthe numbers of colors is selected according to the count results. As aresult, optimal color conversion processing can be executed according toan input image, and the best output can be obtained.

In the above description, the curve tables shown in FIG. 13 are preparedin the density conversion table 1104, and one of these tables isselected by the CPU 1109. However, the present invention is not limitedto the above embodiment. For example, the curve tables shown in FIG. 13may be prepared in the CPU 1109 or in the ROM 1124, and may be set inthe density converter 1104 by the CPU 1109. The CPU 1109 may calculatean optimal curve table, and set the calculated table in the densityconverter 1104, thus obtaining the same effect as described above.

In the above description, the masking coefficients of the masking•UCRcircuit 1105 are changed in correspondence with the curves of thedensity converter 1104 in accordance with ΔE_(max). However, constantmasking coefficients of the masking•UCR circuit 1105 may be used toobtain a good print result. Similarly, nine masking coefficients (if a3×3 matrix is adopted) may be independently changed and selectedaccording to ΔE_(max) in place of being combined with the curves of thedensity converter 1104.

In this arrangement, a good print result can be obtained.

Furthermore, in the above-mentioned selection, an average value ofΔE_(j) may be used in place of ΔE_(max).

Furthermore, as an input apparatus, the external input apparatus, e.g.,a CG (computer graphic) image from a computer, an image input from an SV(still video) camera, a video, or the like may be used. In this case,these signals are input after the A/D converter, as shown in FIG. 11.The CG image can be directly input since it is expressed by digitalsignals. However, the video input must be converted into digital signalsin advance. After these signals are input, they are processed in thesame manner as an original input.

The present invention is not limited to the color copying apparatus, butmay be applied to a color image processing apparatus.

As described above, according to the present invention, since a meansfor detecting a color range of an input image, and a means for changingprocessing according to the detected color range are arranged, a goodcolor conversion result can be obtained for images in every colorranges.

Ninth Embodiment!

The ninth embodiment according to the present invention will bedescribed below with reference to the accompanying drawings.

FIG. 16 is a block diagram of the ninth embodiment according to thepresent invention.

In FIG. 16, the same reference numerals denote the same parts as in FIG.1, and a detailed description thereof will be omitted.

In FIG. 16, reference numeral 161 denotes an input RAM for temporarilystoring input color image signals, and the like; 162, an output RAM fortemporarily storing converted output color image signals, and the like;163, a CPU for controlling the overall apparatus of this embodimentaccording to an internal program; 164, a density converter forperforming density conversion processing of input color image signals;and 165, a masking-UCR circuit.

The density converter 164 and the masking•UCR circuit 165 of thisembodiment have the same arrangement as that of the density converter1104 and the masking•UCR circuit 1105 in the eighth embodiment. In thedensity converter 1104, a plurality of curve tables (e.g., 1 to 4) areprepared, as shown in FIG. 13. In the masking•UCR circuit 165, aplurality of sets of masking coefficients corresponding in number to thecurve tables are prepared.

Color conversion processing of the apparatus of this embodiment with theabove arrangement will be described below with reference to the flowchart shown in FIG. 17.

In step S11, when color image signals based on the additive colorprocess, expressed by three primary colors, i.e., red (R), green (G),and blue (B), are input from an image input apparatus 101, the CPU 163samples some components of the input color image signals, andtemporarily saves them in the input RAM 161. For example, as shown inFIG. 15, components indicated by ◯ of the input color image signals aresampled, and are saved in the input RAM 161.

In step S12, the input image signals are color-converted into colorimage signals based on the corresponding substractive color process bythe densigy converter 164 and the masking•UCR circuit 165. The colorconversion processing is executed by a plurality of kinds of processingmethods using some or all of the plurality of curve tables of thedensity converter 164 shown in FIG. 13, and the plurality of sets ofmasking coefficients of the masking•UCR circuit 165 corresponding innumber to the curve tables.

At this time, the converted color image signals corresponding to thesampling points of the input color image signals, as shown in FIG. 15,are sampled in step S13, and are saved in the output RAM 162. In thiscase, sampled data are saved in units of all the kinds of processingmethods.

In step S14, the number of sets of R, G, and B signals having differentsignal values at the sampling points saved in the input RAM 161 iscounted. The sets of R, G, and B signals having different signal valuesmean different colors. The count value is represented by C₀.

In step S15, the number of sets of color-converted Y, M, C, and Ksignals having different signal values at the sampling points and savedin the output RAM 162 in the first color conversion processing method iscounted. The count value is represented by C₁.

In step S16, it is checked if the color count processing is executed fordata at the sampling points in all the color conversion processingmethods executed in step S13. If NO in step S16, the flow advances tostep S17.

In step Sl7, the next color conversion processing method is selected tocount the sampling points. The flow then returns to step S15, and acount operation of the sampling points in the next processing method isstarted.

In this manner, the numbers of sets of Y, M, C, and K signals havingdifferent signal values obtained in the different processing methods arerespectively represented by, e.g., C₂, C₃, and C₄. The values C₁ to C₄are equal to or smaller than C₀.

In this manner, the sampling points of the color conversion processingoperations by the different processing methods are sequentially conted.If these operations are completed for all the processing methods, theflow advances from step S16 to step S20. In step S20, of the countvalues C₁ to C₄ of the processing methods, a value nearest to the countvalue C₀ of the sampling points of the input color image signals isobtained.

If C_(i) is obtained, it is determined that processing for obtainingC_(i) is best suitable for an input image. For this reason, the CPU 163sets the density converter 164 and the masking•UCR circuit 165 toexecute the ith processing method in step S21.

Upon completion of the setting operation, in step S22, color imagesignals are input again from the image input apparatus, and arecolor-converted by the selected color conversion processing. Morespecifically, R (red), G (green), and B (blue) color signals arecolor-converted into C, M, and Y color signals by the density converter164, and the C, M, and Y color signals are converted into Y (yellow), M(magenta), C(cyan), and K (black) signals by removing color muddiness bythe masking•UCR circuit 165. The color-converted color image signals areoutput to the image output apparatus 103.

As described above, according to this embodiment, the number of colorsof input signals, and the number of post-processing colors of inputsignals, and the number of post-processing colors are counted, and colorconversion processing having the smallest decrease in the number ofcolors is selected, so that optimal color conversion processing can beexecuted in accordance with an input image, and the best output can beobtained.

Tenth Embodiment!

In the ninth embodiment described above, the CPU 163 sets the bestprocessing method in the density converter 164 and the masking•UCRcircuit 165, and color conversion processing is executed based on theset processing method. However, the present invention is not limited tothe above embodiment. For example, a plurality of color conversionprocessing operations may be executed at the same time, and only signalsconverted by the optimal color conversion processing may be selectedfrom those converted by these color conversion processing operations,thus obtaining the same effect as described above.

FIG. 18 shows the arrangement of the tenth embodiment according to thepresent invention.

In FIG. 18, a selector 186 is added to the circuit of the ninthembodiment shown in FIG. 16, and a density converter 184 and amasking•UCR circuit 185 can simultaneously execute a plurality of colorconversion processing operations.

Other arrangements are the same as those in the ninth embodiment shownin FIG. 16, and the control operation is also the same as that in theninth embodiment.

In the tenth embodiment, a CPU 163 may supply a select signal to theselector 186 on the basis of a comparison/discrimination result of countvalues of the numbers of sets having different signal values by the CPU163 so as to select the best color.

When the same count values are obtained upon discrimination, a valuehaving a smaller suffix is selected. For example, when C₁ and C₂ arenearest to C₀ and are equal to each other, C₁ is selected.

Alternatively, as masking coefficients have smaller suffixes, diagonalcomponents a₁₁, a₂₂, and a₃₃ may become close to 1 as follows. ##EQU9##

Furthermore, color conversion processing may be selected using only aplurality of numbers of different post-processing colors without usingthe number of different pre-processing colors. The largest one of thenumbers of different post-processing colors may be selected.

It is effective to execute the above-mentioned processing methodselection algorithm of each of the above embodiments in such a prescanoperation as shown in FIG. 21.

More specifically, in a color copying machine, when an original isplaced on an original table, and a copy start key is depressed, aprescan operation prior to an actual printing operation is normallyexecuted so as to detect, e.g., an original size. In this case, theabove-mentioned algorithm is executed, so that an optimal processingsequence can be executed in the main scan mode.

As described above, according to the present invention, a means forcounting the number of colors of input signals, and the number of colorsafter color conversion processing is arranged, and processing having thesmallest decrease in the number of colors is selected according to thecount results. Thus, an optimal processing method can be selectedaccording to an input image, and a good color-conversion output can beobtained.

Each of the above embodiments can be applied to any copying operationscapable of performing color image formation in, e.g., a leaser beamprinter, an ink-jet printer, and the like.

The image output apparatus 103 may comprise an electrophotography typelaser printer, a sublimation type thermal transfer printer, or anyink-jet type printer.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A color image processing apparatuscomprising:input means for inputting color image data representing acolor image of interest; memory means for storing a color gamut of anoutput device, represented with a hexahedron comprising substantiallyred, green, blue, cyan, magenta, yellow, white and black color-componentpoints; extraction means for extracting a color gamut of the color imageof interest and for determining whether or not the color gamut of thecolor image of interest is within the color gamut of the output device;and color-gamut mapping means for mapping the color image data based onthe result from extraction by the extraction means, wherein saidcolor-gamut mapping means performs mapping in a set mapping mode basedon the result from the extraction by said extraction means, and whereinsaid color-gamut mapping means performs mapping in a first mode in whichcolor image data is reproduced within a color gamut of an output devicewith high fidelity, or performs mapping in a second mode, if the colorimage includes color image data outside of the color gamut of the outputdevice, in which color image data is color-gamut-mapped so as tomaintain contrast of the color image.
 2. The color image processingapparatus according to claim 1, wherein said extraction means extractsthe color gamut of the color image of interest at prescanning time. 3.The color image processing apparatus according to claim 1, furthercomprising:a scanner for inputting the color image data; and imageformation means for forming an image based on the color image datamapped by said color-gamut mapping means.
 4. The color image processingapparatus according to claim 1, wherein said color-gamut mapping meansuses a look-up table for mapping the color image data.
 5. The colorimage processing apparatus according to claim 1, wherein saidcolor-gamut mapping means performs a matrix operation for mapping thecolor image data.
 6. The color image processing apparatus according toclaim 1, wherein said extraction means extracts color distribution ofthe color image data.
 7. A color image processing apparatuscomprising:input means for inputting color image data representing acolor image of interest; selection means for selecting one of pluralmapping modes; and mapping means for color-gamut mapping the color imagedata based on the mapping mode selected by said selection means, whereinsaid plural mapping modes include:a first mode for reproducing the colorimage data within a color gamut of an output device so that the colorimage data has a high fidelity; a second mode for mapping color imagedata outside of the color gamut of the output device into the colorgamut of the output device; and a third mode for mapping the color imagedata so as to enlarge a gamut of the color image of interest.
 8. Thecolor image processing apparatus according to claim 7, wherein the thirdmode is directed to a map image.
 9. The color image processing apparatusaccording to claim 7, wherein said selection means selects a mappingmode in accordance with manual operation.
 10. The color image processingapparatus according to claim 7, wherein said selection meansautomatically selects a mapping mode.
 11. The color image processingapparatus according to claim 7, wherein in the first mode, a look-uptable is used for mapping the color image data.
 12. The color imageprocessing apparatus according to claim 7, wherein in the second mode, amatrix operation is performed for mapping the color image data.
 13. Thecolor image processing apparatus according to claim 7, wherein in thesecond mode, one of plural color-gamut mapping methods is used incorrespondence with the color gamut of the color image data.
 14. Thecolor image processing method according to claim 7, further comprisingimage formation means for forming an image based on the color image datamapped by said color-gamut mapping means.
 15. A color image processingapparatus comprising:input means for inputting color image datarepresenting a color image of interest; memory means for storingcolor-gamut mapping data corresponding to a plurality of color gamuts;extraction means for extracting information on a color gamut of thecolor image of interest; setting means for automatically setting thecolor-gamut mapping data based on the information on the color gamut ofthe image data; and color-gamut mapping means for mapping the colorimage data based on the color-gamut mapping data set by said settingmeans.
 16. The color image processing apparatus according to claim 15,wherein the color-gamut mapping data is indicative of matrixcoefficients.
 17. The color image processing apparatus according toclaim 15, wherein said extraction means extracts the color gamut of theimage data at prescanning time.
 18. The color image processing apparatusaccording to claim 15, wherein the color-gamut mapping data isindicative of a look-up table.
 19. The color image processing methodaccording to claim 15, further comprising image formation means forforming an image based on the color image data mapped by saidcolor-gamut mapping means.
 20. A color processing method comprising:aninput step of inputting color image data representing a color imageinterest; a selection step of selecting one of plural mapping modes; anda mapping step of mapping the color image data based on the mapping modeselected in said selection step, wherein said plural mapping modesinclude:a first mode for reproducing color image data with a highfidelity within a color gamut of an output device; a second mode formapping color image data outside of the color gamut of the output deviceinto the color gamut of the output device; and a third mode for mappingthe color image data so as to enlarge a gamut of the color image ofinterest.
 21. A color image processing method comprising:an input stepof inputting color image data representing a color image of interest; amemory step of storing color-gamut mapping data corresponding to aplurality of color gamuts; an extraction step of extracting informationon a color gamut of the color image of interest; a setting step ofautomatically setting the color-gamut mapping data based on theinformation on the color gamut of the image data; and a color gamutmapping step of mapping the color image data based on the color-gamutmapping data set in said setting step.